Review
- 2024-03-06 23:16
一、Introduction #
Functions are prevalent in Rust code. Rust code uses snake case as the conventional style for function and variable names, in which all letters are lowercase and underscores separate words.
fn main() {
println!("Hello, world!");
another_function(5);
}
fn another_function(x: i32) {
println!("Another function.{}", x);
}We can define functions to have parameters, which are special variables that are part of a function’s signature. When a function has parameters, you can provide it with concrete values for those parameters. Technically, the ==concrete values== are called arguments, but in casual conversation, people tend to use the words parameter and argument interchangeably for either the variables in a function’s definition or the concrete values passed in when you call a function.
Rust is an expression-based language, this is an important distinction to understand.
- Statements are instructions that perform some action and do not return a value.
- Expressions evaluate to a resultant value.
The 6 in the statement let y = 6; is an expression that evaluates to the value 6. Calling a function is an expression. Calling a macro is an expression. A new scope block created with curly brackets is an expression, for example:
fn main() {
let y = {
let x = 3;
x + 1
};
println!("The value of y is: {y}");
}Expressions do not include ending semicolons. If you add a semicolon to the end of an expression, you turn it into a statement, and it will then not return a value. Keep this in mind as you explore function return values and expressions next.
Functions can return values to the code that calls them. We don’t name return values, but we must declare their type after an arrow (->). In Rust, the return value of the function is synonymous with ==the value of the final expression== in the block of the body of a function.